1. Field of the Invention
This invention relates to dimeric compounds comprising two 5-amino-5,6,7,8-tetrahydroquinoline fragments joined together by a divalent linking group, processes for their preparation, intermediates for their preparation, pharmaceutical compositions containing such dimeric compounds and the use of such compounds as cholinesterase inhibitors and in the treatment of neurodegenerative diseases, such as Alzheimer""s Disease and myasthenia gravis.
2. Description of Related Art
Huperzine A is a selective and potent reversible acetylcholinesterase (AChE) inhibitor isolated from the club moss Huperzia serrata which shows considerable promise for the palliative treatment of Alzheimer""s Disease. 
Total syntheses of the racemate and asymmetric syntheses of huperzine A have been reported (see for instance, Xia, Y.; Kozikowski, A. P; J. Am. Chem. Soc. 1989, 111, 4116-4117; Qian, L.; Ji, R.; Tetrahedron Lett. 1989, 30, 2089-2090; Yamada, F.; Kozikowski, A. P.; Reddy, E. R.; Pang, Y-P.; Miller, J. H.; McKinney, M.; J. Am. Chem. Soc. 1991, 113, 4695-4696; Kaneko, S.; Yoshino, T.; Katoh, T.; Terashima, S.; Tetrahedron 1998, 54, 5471-5484; and He, X.-C.; Wang, B.; Bai, D.; Tetrahedron Lett. 1998, 39, 411-414. However, these-syntheses require a minimum of 12 steps.
Enormous effort has also been directed towards the development of more easily synthesised analogues which might prove to. be. more potent than huperzine A. More than 100 such analogues have been disclosed in the scientific and patent literature. For instance, U.S. Pat. No. 5,929,084 discloses huperzine A derivatives in which the hydrogen atom at the 1-position in huperzine A is optionally replaced by a C1-5 alkyl, pyridoyl or C1-5 alkoxy-substituted benzoyl group and the amino group at the 5-position in huperzine A is replaced by a group xe2x80x94N(Rxe2x80x3)YR where Y is a carbonyl group, Rxe2x80x3 is a hydrogen atom or a C1-5 alkyl group, or Rxe2x80x3 and Y together form a group xe2x95x90CH, and R is a C1-5 alkyl or an optionally substituted phenyl, benzyl, naphthyl or pyridyl group. U.S. Pat. No. 5,547,960 discloses huperzine A derivatives which are mono- or disubstituted at the 10-position. Substitution at other positions of the huperzine A molecule is also contemplated in U.S. Pat. No. 5,547,960 but no examples of any such compounds are provided. However, to date, the only huperzine A analogues which have shown superior potency relative to the natural product feature the judicious addition of one or two methyl groups at the 10-position. In this respect, the compounds of formula A above in which R is methyl and Rxe2x80x2 is hydrogen and both R and Rxe2x80x2 are methyl are 8- and 1.4-fold more potent than huperzine A respectively. However, the syntheses of these compounds are longer than that of the natural product.
Removal of the three carbon bridge (C-6 to C-8) from huperzine A has also been explored (see, for instance Kozikowski, A. P.; Miller, C. P.; Yamada, F.; Pang, Y-P.; Miller, J. H.; McKinney, M.; Ball, R. G.; J. Med. Chem. 1991, 34, 3399-3402; Bai. D.; Pure and Appl. Chem. 1993, 65, 1103-1112; and Fink. D. M.; Bores, G. M.; Effland, R. C.; Huger, F. P.; Kurys, B. E.; Rush, D. K.; Selk, D. E.; J. Med. Chem. 1995, 38, 3645-3651). However, in general, these derivatives are very weak AChE inhibitors (IC50 generally  greater than 100,000 nM). Similarly, U.S. Pat. No. 5,110,815 discloses certain 5-amino-5,6,7,8-tetrahydroquinolines which are said to inhibit AChE and relieve memory dysfunction. However, the compounds disclosed are very weak AChE inhibitors (IC50 values in the range of 3.1 to 9.6 xcexcM).
Another AChE inhibitor which has been approved for use in the US for the palliative treatment of Alzheimer""s Disease is 9-amino-1,2,3,4-tetrahydroacridine, also known as THA or tacrine. However, tacrine is a weaker AChE inhibitor than huperzine A and the use of tacrine is currently limited by its peripheral toxicity.
Various compounds have been synthesised which contain tacrine moieties in the search for further efficacious AChE inhibitors. For instance, U.S. Pat. No. 5,783,584 discloses certain alkylene-linked bis-tacrine compounds which are much more potent and much more selective for AChE inhibition than monomeric tacrine. However, despite the increased anti-AChE potency of these bis-tacrine compounds, the very presence of two tacrine moieties in such molecules is likely to cause some significant residual toxicity.
U.S. Pat. No. 5,886,007 discloses tacrine derivatives in which the amino group at the 9-position is substituted by an aralkyl group. These compounds also inhibit AChE but are generally less active than monomeric tacrine and 100- to 15000-fold less active than the compounds of U.S. Pat. No. 5,783,584.
Similarly, Carlier, P. R.; Du, D-M.; Han,Y.;Lin, J.; Pang, Y-P.; Bioorg. Med. Chem. Lett. 1999, 9, 2335-2338, discloses tacrine derivatives in which the amino group at the 9-position is attached to a 5-amino-5,6,7,8-tetrahydro-2(1H)-quinolone moiety by an alkylene chain. However, whilst these compounds are stronger inhibitors of AChE than monomeric tacrine, they are not as potent as the compounds of U.S. Pat. No. 5,783,584. Moreover, like the compounds of U.S. Pat. No. 5,886,007, these compounds still contain one tacrine moiety and are therefore likely to exhibit toxicity problems.
It has now been surprisingly discovered that dimeric compounds containing two 5-amino-5,6,7,8-tetrahydroquinoline or similar moieties joined together by a divalent linking group exhibit high potency as cholinesterase, especially AChE, inhibitors despite the fact that the activity of the constituent 5-amino-5,6,7,8-tetrahydroquinoline or similar monomers is extremely low. Indeed, the optimum dimers are twice as potent as huperzine A. Moreover, such dimeric compounds do not contain any toxic tacrine moieties and can be synthesised in just nine steps from commercially available starting materials.
According to the present invention there is therefore provided a dimeric compound comprising two fragments, which may be the same or different, joined together by a divalent linking group, each fragment having a nucleus of the general formula 
which may be substituted or unsubstituted, in which Q represents the number of carbon atoms necessary to form a 5,6 or 7-membered ring;
R1 represents a hydrogen atom or an optionally substituted alkyl group;
xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group
xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 or Nxe2x95x90C(OR3)xe2x80x94, where R2 represents a hydrogen atom or an optionally substituted alkyl, alkenyl, alkynyl or aralkyl group, and R3 represents a hydrogen atom or an optionally substituted alkyl or aralkyl group; or a salt thereof.
Suitable salts include acid addition salts and these may be formed by reaction of a suitable compound of formula I with a suitable acid, such as an o organic acid or a mineral acid, which is pharmaceutically acceptable. Pharmaceutically acceptable acid addition salts formed by reaction with a mineral acid are particularly preferred, especially salts formed by reaction with hydrochloric or hydrobromic acid. However, pharmaceutically acceptable acid addition salts formed by reaction with an organic acid are also preferred. Suitable organic acids include monobasic carboxylic acids, such as ethanoic and propanoic acid, dibasic carboxylic acids, such as maleic, tartaric, fumaric and oxalic acids, and tribasic carboxylic acids, such as carboxysuccinic and citric acid. Salts formed by reaction with tartaric, fumaric or oxalic acid are also preferred.
Any alkyl, alkenyl or alkynyl group, unless otherwise specified, may be linear or branched and may contain up to 12, preferably up to 6, and especially up to 4 carbon atoms. Preferred alkyl groups are methyl, ethyl, propyl and butyl. When an alkyl moiety forms part of another group, for example the alkyl moiety of an aralkyl group, it is preferred that it contains up to 6, especially up to 4, carbon atoms. Preferred alkyl moieties in this respect are methyl and ethyl.
An aryl group may be any aromatic monocylic or polycyclic hydrocarbon group and may contain from 6 to 24, preferably 6 to 18, more preferably 6 to 16, and especially 6 to 14, carbon atoms. Preferred aryl groups include phenyl, naphthyl, anthryl, phenanthryl and pyryl groups, especially a phenyl. or naphthyl, and particularly a phenyl, group. When an aryl moiety forms part of another. group, for example the aryl moiety of an aralkyl group, it is preferred that it is a phenyl, naphthyl, anthryl, phenanthryl or pyryl, especially a phenyl or naphthyl, and particularly a phenyl, moiety.
An aralkyl group may be any alkyl group substituted by an aryl group. A preferred aralkyl group contains from 7 to 16, especially 7 to 11, carbon atoms, a particularly preferred aralkyl group being a benzyl group.
When any of the foregoing substituents are designated as being optionally substituted, the substituent groups which are optionally present may be any one or more of those customarily employed in the development of pharmaceutical compounds and/or the modification of such compounds to influence their structure/activity, stability, bioavailability or other property. Specific examples of such substituents include, for example, halogen atoms, nitro, cyano, hydroxyl, cycloalkyl, alkyl, haloalkyl, cycloalkyloxy, alkoxy, haloalkoxy, amino, alkylamino, dialkylamino, formyl, alkoxycarbonyl, carboxyl, alkanoyl, alkylthio, alkylsulphinyl, alkylsulphonyl, alkylsulphonato, arylsulphinyl, arylsulphonyl, arylsulphonato, carbamoyl, alkylamido and heterocyclic groups. When any of the foregoing substituents represents or contains an alkyl substituent group, this may be linear or branched and may contain up to 12, preferably up to 6, and especially up to 4, carbon atoms. A cycloalkyl group may contain from 3 to 8, preferably from 3 to 6, carbon atoms. An aryl group or moiety may contain from 6 to 10 carbon atoms, phenyl groups being especially preferred. A halogen atom may be a fluorine, chlorine, bromine or iodine atom and any group which contains a halo moiety, such as a haloalkyl group, may thus contain any one or more of these halogen atoms.
In a particularly preferred group of compounds Q represents one carbon atom which may be substituted or unsubstituted. Thus, the nucleus of general formula I is a 5-amino-5,6,7,8-tetrahydroquinoline moiety. Preferably, Q represents one carbon atom in both fragments of the dimeric compound. However, it is also envisaged that Q may represent a different number of carbon atoms in each fragment.
It is preferred that R1 represents a hydrogen atom or a C1-4 alkyl group, preferably unsubstituted. More preferably, R1 represents a hydrogen atom.
In one preferred group of compounds xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(2)xe2x80x94C(O)xe2x80x94. Preferably, R2 represents a hydrogen atom or C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl or C7-6 aralkyl, preferably C7-11 aralkyl, group More preferably, R2 represents a hydrogen atom or a C1-4 alkyl, especially methyl, group.
In another preferred group of compounds xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94. Preferably, R3 represents a hydrogen atom or a C1-6 alkyl or C7-6 aralkyl group. More preferably, R3 represents a C1-4 alkyl, especially methyl, or a C7-11 aralkyl, especially benzyl group.
The saturated ring of the nucleus of general formula I may be unsubstituted. Alternatively, the saturated ring of the nucleus of general formula I may be substituted at one or more of the available carbon atoms by one or more substituents of formula R4. Thus, the nucleus of general formula I may be further defined by the general formula 
in which Q, R1 and xe2x80x94Wxe2x80x94Xxe2x80x94 are as previously defined, m is 0 or an integer from 1 to (2pxe2x88x925) where p is the number of carbon atoms in the saturated ring of the nucleus, and each substituent R4 independently represents an optionally substituted alkyl or aralkyl group. Thus, when the saturated ring contains five carbon atoms (Q represents a single bond), m is 0 or an integer from 1 to 5; when Q represents one carbon atom, m is 0 or an integer from 1 to 7; and when Q represents two carbon atoms, m is 0 or an integer from 1 to 9. More preferably, m is 0 or an integer from 1 to 3. When the saturated ring of the nucleus of general formula I is substituted, it is preferred that two substituents R4 are located at the 7-position of the nucleus and/or that one substituent R4 is located at the 5-position of the nucleus. Preferably, each substituent R4 independently represents a C1-4 alkyl, especially a methyl, group.
It is preferred that the two fragments having a nucleus of the general formula I are the same as one another, that is, the dimeric compounds of the invention are homodimers. However, it is also envisaged that the two fragments having a nucleus of general formula I may be different from one another, that is, the dimeric compounds of the invention are heterodimers. In the case of heterodimers, the two fragments may differ only in optional substituents on the saturated ring of the nucleus or they may differ in fundamental size, structure and substituents as defined in relation to formula I.
The divalent linking group may be any group which is capable of linking the 5-amino groups of the two fragments having a nucleus of the general formula I. However, it is preferred that the divalent linking group is an optionally substituted alkylene chain which is optionally interrupted by one or more heteroatoms, such as oxygen, sulphur and nitrogen atoms, or optionally substituted aryl groups. Preferably, the optionally substituted alkylene chain is optionally interrupted by one or more moieties selected from xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NRxe2x80x94, xe2x80x94COxe2x80x94 and optionally substituted aryl, especially C6-14 aryl, groups, where R represents a hydrogen atom or an optionally substituted alkyl, preferably C1-4 alkyl and especially methyl, group. More preferably, R represents a hydrogen atom.
It is particularly preferred that the optionally substituted alkylene chain is optionally interrupted by one or more moieties selected from xe2x80x94Oxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94C(O)xe2x80x94, phenyl and naphthyl groups. It is also preferred that the optionally substituted alkyl chain has a chain length of 2 to 16, preferably 4 to 14, and especially 6 to 12, atoms.
Preferably, the divalent linking group is an alkylene chain, a rigidified hydrocarbon linker, a polyethylene glycol linker, an oxalic diamide linker or a urea linker. A rigidified hydrocarbon linker is a hydrocarbon chain which is rigidified by the inclusion of an aryl moiety in the chain. A polyethylene glycol linker is a linker including one or more xe2x80x94Oxe2x80x94CH2xe2x80x94CH2xe2x80x94 units. An oxalic diamide linker is a linker including one or more xe2x80x94NHxe2x80x94C(O)xe2x80x94C(O)xe2x80x94NHxe2x80x94 units. A urea linker includes one or more xe2x80x94NHxe2x80x94C(O)xe2x80x94NHxe2x80x94 units. In the case of oxalic diamide and urea linkers, a xe2x80x94NHxe2x80x94C(O)xe2x80x94C(O)xe2x80x94NHxe2x80x94 or xe2x80x94NHxe2x80x94C(O)xe2x80x94NHxe2x80x94 unit must be separated from the 5-amino group of the fragments having a nucleus of the general formula I by at least two methylene groups. Also, if more than one xe2x80x94NHxe2x80x94C(O)xe2x80x94C(O)xe2x80x94NHxe2x80x94 or xe2x80x94NHxe2x80x94C(O)xe2x80x94NHxe2x80x94 unit is present in the divalent linking group, the units must be separated from one another by at least two methylene groups.
Especially preferred divalent linking groups include optionally substituted alkylene groups of formula xe2x80x94(CH2)nxe2x80x94 where n is an integer from 2 to 16, preferably 4 to 14 and especially 6 to 12; rigidified hydrocarbon linkers of formula xe2x80x94(CH2)qxe2x80x94Arxe2x80x94(CH2)rxe2x80x94 where q and r are each independently 0 or an integer from 1 to 5, preferably 1 to 4 and especially 1 or 2, and Ar represents an optionally substituted C6-14 aryl, preferably C6-10 aryl and especially phenyl or naphthyl, group; and of formula xe2x80x94(CH2)sxe2x80x94Ar1xe2x80x94Bxe2x80x94Ar2xe2x80x94(CH2)txe2x80x94 where s and t are each independently 0 or an integer from 1 to 3, especially 1 or 2, Ar1 and Ar2 each independently represent an optionally substituted C6-14 aryl, preferably C6-10 aryl and especially phenyl or naphthyl, group and B represents a group xe2x80x94(CH2)u where u is 0,1,2 or 3, especially 0 or 2, xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94; polyethylene glycol linkers of formula xe2x80x94CH2CH2xe2x80x94(OCH2CH2)vxe2x80x94 where v is an integer from 1 to 4, especially 2 or 3; oxalic diamide linkers of formula xe2x80x94(CH2)wxe2x80x94NHxe2x80x94C(O)xe2x80x94C(O)xe2x80x94NHxe2x80x94(CH2)xxe2x80x94 where w and x independently represent an integer from 2 to 6, preferably 2 to 5 and especially 3 to 5; and urea linkers of formula xe2x80x94(CH2)y"Brketopenst"NHxe2x80x94C(O)xe2x80x94NHxe2x80x94(CH2)z"Brketclosest"a where y and z independently represent an integer from 2 to 6, especially 3 to 5, and a represents an integer from 1 to 3.
Specific preferred linkers include the following: 
The numbers given above indicate the effective chain length of the divalent linking group.
Although the divalent linking groups shown above have been shown as containing one or more methylene groups xe2x80x94CH2xe2x80x94, each of these methylene groups may be optionally substituted by any of the optional substituents listed above, preferably C1-4 alkyl, and especially methyl, groups. However, it is preferred that these divalent linking groups are unsubstituted.
Preferably, the divalent linking group is an unsubstituted alkylene chain of formula xe2x80x94(CH2)nxe2x80x94 in which n is an integer from 2 to 16, preferably 4 to 14, and especially 6 to 12, carbon atoms. It is particularly preferred that n is an integer from 9 to 12.
In a particularly preferred sub-group of the dimeric compounds of the invention, both fragments are the same, Q represents an unsubstituted carbon atom, R1 represents a hydrogen atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 where R2 represents a hydrogen atom or a methyl group , the saturated ring of the nucleus of formula I is unsubstituted or substituted at the 7-position by two methyl groups and/or at the 5-position by one methyl group, and the divalent linking group is an unsubstituted alkylene chain of formula xe2x80x94(CH2)nxe2x80x94 where n is an integer from 4 to 14.
N,Nxe2x80x2-Di-5xe2x80x2-(5xe2x80x2,6xe2x80x2,7xe2x80x2,8xe2x80x2-tetrahydroquinolin-2-onyl)-1,12-diaminododecane, N,Nxe2x80x2-di-5xe2x80x2-(5xe2x80x2,6xe2x80x2,7xe2x80x2,8xe2x80x2-tetrahydroquinolin-2-onyl)-1,13-diaminotridecane and salts thereof are especially preferred.
In another particularly preferred sub-group of the dimeric compounds of the invention, both fragments are the same, Q represents an unsubstituted carbon atom, R1 represents a hydrogen atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94 where R3 represents a methyl or benzyl group, the saturated ring of the nucleus of formula I is unsubstituted or substituted at the 5-position by one methyl group, and the divalent linking group is an unsubstituted alkylene chain of formula xe2x80x94(CH2)nxe2x80x94 where n is an integer from 4 to 14, preferably 10 or 12.
N,Nxe2x80x2-Di-5xe2x80x2-(5xe2x80x2,6xe2x80x2,7xe2x80x2,8xe2x80x2-tetrahydro-2xe2x80x2-methoxyquinolinyl)-1,10-diaminodecane, N,Nxe2x80x2-di-5xe2x80x2-(5xe2x80x2,6xe2x80x2,7xe2x80x2,8xe2x80x2-tetrahydro-2xe2x80x2-methoxyquinolinyl)-1,12-diaminododecane and salts thereof are especially preferred.
It should also be appreciated that the fragments having a nucleus of general formula I contain chiral centres and the dimeric compounds of the invention are therefore capable of existing as different optical isomers. Moreover, if these fragments or the divalent linking group contain an alkenyl group, the dimeric compounds are also capable of existing as different geometric isomers. The present invention thus includes both the individual isomers and mixtures of such isomers. Enantiomers of the dimeric compounds of the invention are particularly preferred, especially the (S,S)- and (R,R)-enantiomers. However, (R,S)-stereoisomers may be present in a mixture with the racemic mixture of (S,S)- and (R,R)-enantiomers and are also included within the present invention.
The present invention also provides a process for the preparation of a dimeric compound according to the invention as defined above which comprises. reacting two compounds, which may be the same or different, having a nucleus of the general formula 
which may be substituted or unsubstituted, in which Q and xe2x80x94Wxe2x80x94Xxe2x80x94 are as defined above, or a salt thereof, with a compound of the general formula
HR1Nxe2x80x94Axe2x80x94NR1Hxe2x80x83xe2x80x83(III)
in which each R1 is independently as defined above and A represents a divalent linking group as defined above and, either reducing the bis-imine compound so formed to produce a dimeric compound as defined above which is unsubstituted at the 5-position, or reacting the bis-imine compound so formed with a suitable organometallic reagent to produce a dimeric compound as defined above which is substituted at the 5-position; and, if desired, when xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94 and R3 represents an optionally substituted arylmethyl group in at least one of the compounds having a nucleus of general formula II, subjecting the dimeric compound so formed to hydrogenolysis to produce a dimeric compound in which both moieties xe2x80x94Wxe2x80x94Xxe2x80x94 represent a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94.
The reaction of the two compounds having a nucleus of formula II with the compound of formula III may be conveniently carried out in the presence of a suitable solvent. Suitable solvents include aromatic solvents, such as benzene or toluene. Preferably, the reaction is carried out at the reflux temperature of the solvent, preferably in the presence of a catalyst, such as ethanoic acid, to form the bis-imine compound in situ.
Reduction of the bis-imine compound to produce a dimeric compound which is unsubstituted at the 5-position is carried out by reaction with a suitable reducing agent. Suitable reducing agents include sodium borohydride in methanol.
Alternatively, suitable organometallic reagents for reacting with the bis-imine compound to form a dimeric compound which is substituted at the 5-position include organolithium reagents and Grignard reagents. This reaction may be carried out in the presence or absence of a suitable Lewis acid depending on the organometallic reagent selected. If required, suitable Lewis acids include boron trifluoride, aluminium chloride and titanium tetrachloride.
Hydrogenolysis of dimeric compounds which contain a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94, where R3 represents an optionally substituted arylmethyl group in at least one of the compounds having a nucleus of formula II, to produce a dimeric compound in which both moieties xe2x80x94Wxe2x80x94Xxe2x80x94 represent a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 may be carried out using a suitable hydrogenating agent, such as hydrogen gas in the presence of palladium on carbon, in a suitable solvent, such as ethanol. Preferably, R3 represents a benzyl group.
Compounds having a nucleus of formula II in which xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 where R2 is a hydrogen atom may be conveniently prepared by condensing a compound having a nucleus of the general formula 
in which Q is as defined above, with methyl propiolate according to the methods of Dubas-Sluyter, M. A. T.; Speckarnp, W. N.; Huisman H. O.; Recueil, 1972, 91,157-160 and Zacharias, G.; Wolfbeis, O. S.; Junek, H.; Monatsch, Chem., 1974, 105, 1283-1291. The reaction is preferably carried out at a temperature in the range of 100 to 180, preferably 110 to 170xc2x0 C.
Compounds having a nucleus of formula VI may be conveniently prepared by reacting a compound having a nucleus of the general formula 
in which Q is as defined above, with ammonia in a suitable solvent, such as benzene or toluene, suitably at reflux temperature.
Compounds having a nucleus of formula II in which xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 where R2 is other than a hydrogen atom may be prepared by reacting a compound having a nucleus of formula II in which xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 where R2 is a hydrogen atom with a compound of formula R2xe2x80x2Y where R2xe2x80x2 is a suitable alkyl, alkenyl, alkynyl or aralkyl group and Y represents a suitable halogen atom in the presence of sodium methoxide and a suitable solvent, such as tetrahydrofuran, at reflux temperature.
Compounds having a nucleus of formula II in which xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94 where R3 is as defined above may be prepared by reacting a compound having a nucleus of formula II in which xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94, where R2 is a hydrogen atom, with a compound of formula R3Y where R3 is as defined above and Y is a suitable halogen atom. The reaction is conveniently carried out in the presence of silver carbonate in a suitable solvent, such as trichloromethane or toluene. Preferably, the reaction is carried out at room temperature, that is 15 to 35xc2x0 C., preferably 20 to 30xc2x0 C.
Compounds of formulae III and VII are known compounds or can be prepared by methods analogous to known processes.
In another aspect, the present invention provides a process for the preparation of a dimeric compound according to the invention as defined above which comprises reacting two compounds, which may be the same or different, having a nucleus of the general formula 
which may be substituted or unsubstituted, in which Q, R1 and xe2x80x94Wxe2x80x94Xxe2x80x94 are as defined above, or a salt thereof, with a compound of the general formula
Lxe2x80x94COxe2x80x94A1xe2x80x94COxe2x80x94Lxe2x80x83xe2x80x83(V)
in which each L independently represents a hydrogen atom or a leaving group Y of which the conjugate acid HY has a pKa value which is less than or equal to 10 and xe2x80x94COxe2x80x94A1xe2x80x94COxe2x80x94 represents a group which forms a divalent linking group as defined above in the resultant dimeric compound; if desired, reducing the dimeric compound so formed to produce a further dimeric compound as defined above;
and, if desired, when xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94 and R3 represents an optionally substituted arylmethyl group in at least one of the compounds having a nucleus of general formula IV, subjecting the dimeric compound so formed to hydrogenolysis to. produce a dimeric compound in which both moieties xe2x80x94Wxe2x80x94Xxe2x80x94 represent a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94. This process is particularly suitable for preparing dimeric compounds which are substituted at the 5-position by substituent R4.
The reaction of the two compounds having a nucleus of formula IV with the compound of formula V may be conveniently carried out in the presence of a suitable solvent. Suitable solvents include aromatic solvents, such as benzene. Preferably, the reaction is carried out in the presence of a catalyst, such as ethanoic acid, preferably at the reflux temperature of the reaction mixture.
When L is a hydrogen atom, a bis-imine is formed in situ which can be reduced to produce a dimeric compound according to the invention using a suitable reducing agent, such as sodium borohydride in methanol, as described above. However, when L is other than a hydrogen atom, for instance a chlorine atom, no reduction is required.
Hydrogenolysis of dimeric compounds which contain a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94, where R3 represents an optionally substituted arylmethyl group in at least one of the compounds having a nucleus of formula IV to produce a dimeric compound in which both moieties xe2x80x94Wxe2x80x94Xxe2x80x94 represent a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 may be carried out as described above.
Compounds having a nucleus of formula IV which bear a substituent at the 5-position in which xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94, where R3 represents an optionally substituted arylmethyl group, may be conveniently prepared by reacting a compound having a nucleus of formula II in which xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90(OR3)xe2x80x94, where R3 represents an optionally substituted arylmethyl group, with a suitable Grignard reagent in a suitable solvent, such as tetrahydrofuran, at a suitable temperature, such as room temperature, that is, 15 to 35xc2x0 C., preferably 20 to 30xc2x0 C. The resultant tertiary alcohol compound may then be reacted with O-arylmethylhydroxylamine in a suitable solvent, such as toluene, in the presence of trifluoroethanoic acid at a suitable temperature, such as room temperature. The desired compound may then be obtained by treating the resultant compound with borane-tetrahydrofuran at a temperature in the range from 0xc2x0 C. to the reflux temperature of the reaction mixture.
Compounds having a nucleus of formula IV which bear no substituent at the 5-position and in which xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90C(OR3), where R3 represents an optionally substituted arylmethyl group, may be conveniently prepared by reacting a compound having a nucleus of formula II in which xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94, where R3 represents an optionally substituted arylmethyl group, with hydroxylamine or O-benzylhydroxylamine in pyridine, and subsequent reduction with active metal reducing agents (such as Raney Nickel and hydrogen gas) or borane respectively.
Compounds of formulae V are known compounds or can be prepared by methods analogous to known processes.
U.S. Pat. No. 5,110,815 discloses some compounds having a nucleus of the general formula II, namely, 5,6,7,8-tetrahydro-5-oxo-2-(phenylmethoxy)quinoline; 5,6,7,8-tetrahydro-5-oxo-2(1H)-quinolinone; 5,6,7,8-tetrahydro-1-methyl-5-oxo-2(1H)-quinolinone; 5,6,7,8-tetrahydro-5-oxo-1-(2-propenyl)-2(1H)-quinolinone; 5,6,7,8-tetrahydro-5-oxo-1-phenylmethyl-2(1H)-quinolinone; 5,6,7,8-tetrahydro-7,7-dimethyl-5-oxo-2(1H)-quinolinone; 1,7,7-trimethyl-5-oxo-2(1H)-quinolinone; 5,6,7,8-tetrahydro-1-propyl-5-oxo-2(1H)-quinolinone; 1-hexyl-5,6,7,8-tetrahydro-5-oxo-2(1H)-quinolinone; 5,6,7,8-tetrahydro-1-(3-methyl-2-butenyl)-5-oxo-2(1H)-quinolinone and 5,6,7,8-tetrahydro-5-oxo-1-(2-phenylethyl)-2(1H)-quinolinone. However, certain compounds having a nucleus of general formula II are novel. The present invention therefore also provides a compound having a nucleus of the general formula 
which may be substituted or unsubstituted, or a salt thereof, in which Q and xe2x80x94Wxe2x80x94Xxe2x80x94 are as defined above; with the provisos that
(i) when Q represents one carbon atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94 and the nucleus of formula II is unsubstituted, then R3 does not represent a benzyl group;
(ii) when Q represents one carbon atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 and the nucleus of formula II is unsubstituted, then R2 does not represent a hydrogen atom or a methyl, propyl, hexyl, 2-propenyl, 3-methyl-2-butenyl, benzyl or 2-phenylethyl group; and
(iii) when Q represents one carbon atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 and the nucleus of formula II is substituted at the 7-position by two methyl groups, then R2 is not a hydrogen atom or a methyl group.
Compounds in which Q represents one carbon atom and xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94 where R3 represents a methyl group are particularly preferred. Of these, 5,6,7,8-tetrahydro-2-methoxy-5-oxo-quinoline and salts thereof are especially preferred.
U.S. Pat. No. 5,110,815 also discloses some compounds having a nucleus of the general formula IV, namely 5,6,7,8-tetrahydro-5-methyl-2-(phenylmethoxy)-5-quinolinamine hemifumarate; 5,6,7,8-tetrahydro-5-amino-5-methyl-2(1H)-quinolinone hydrochloride; 5,6,7,8-tetrahydro-5-amino-1,5-dimethyl-2(1H)-quinolinone; 5,6,7,8-tetrahydro-N,5-dimethyl-2-(phenylmethoxy)-5-quinolinamine; 5,6,7,8-tetrahydro-5-methyl-5-(methylamino)-2(1H)-quinolinone hydrochloride; 5,6,7,8-tetrahydro-2-(phenylmethoxy)-5-(phenylmethyl)-5-quinolinamine; 5-amino-5,6,7,8-tetrahydro-5-(phenylmethyl)-2(1H)-quinolinone hydrochloride; 5,6,7,8-tetrahydro-5-[-(2-phenyethyl)amino]-2(1H)-quinolinone hydrochloride; 5,6,7,8-tetrahydro-1-methyl-5-[(2-phenylethyl)amino]-2(1H)-quinolinone dihydrochloride monohydrate; 5,6,7,8-tetrahydro-5-oxo-2-(phenylmethoxy)quinoline oxime benzyl ether; 5,6,7,8-tetrahydro-5-[(2-phenylethyl)amino]-1-(2-propenyl)-2(1H)-quinolinone; 5-[[2-(3,4-dichlorophenyl)ethyl]amino]-5,6,7,8-tetrahydro-1-(2-propenyl)-2(1H)-quinolinone fumarate; 5,6,7,8-tetrahydro-5-[(2-phenylethyl)-amino]-1-propyl-2(1H)-quinolinone fumarate; 5-[[2-(3,4-dichlorophenyl)-ethyl]amino]-5,6,7,8-tetrahydro-1-(phenylmethyl)-2(1H)-quinolinone fumarate; 5,6,7,8-tetrahydro-1-methyl-5-[(phenylmethyl)amino]-2(1H)-quinolinone fumarate; 5-[[2-(4-trifluromethylphenyl)ethyl]amino]-5,6,7,8-tetrahydro-1-methyl-2(1H)-quinolinone; 5,6,7,8-tetrahydro-1-methyl-5-[[2-(4-nitrophenyl)ethyl]amino]-2(1H)-quinolinone; 5-[[2-(4-chlorophenyl)ethyl]amino]-5,6,7,8-tetrahydro-1-methyl-2(1H)-quinolinone; 5,6,7,8-tetrahydro-5-[[2-(4-methoxyphenyl)ethyl]amino]-1-methyl-2(1H)-quinolinone; 5,6,7,8-tetrahydro-1-methyl-5-[[2-(4-methylphenyl)-ethyl]amino]-2(1H)-quinolinone fumarate; 5-[[2-(2,4-dichlorophenyl)ethyl]amino]-5,6,7,8-tetrahydro-1-methyl-2(1H)-quinolinone; 5-[[2-(3,4-dichlorophenyl)ethyl]-amino]-5,6,7,8-tetrahydro-1-methyl-2(1H)-quinolinone; 5,6,7,8-tetrahydro-1-methyl-5-[[2-(2,2-diphenyl)ethyl]amino]-2(1H)-quinolinone; 5,6,7,8-tetrahydro-1-methyl-5-[(3-phenylpropyl)amino]-2(1H)-quinolinone flumarate; 5-[[2-(4-chlorophenyl)-ethyl]amino]-5,6,7,8-tetrahydro-1,7,7-trimethyl-2(1H)quinolinone fumarate; 5-[[2-(3,4-dichlorophenyl)ethyl]amino]-5,6,7,8-tetrahydro-1-propyl-2(1H)-quinolinone; 5,6,7,8-tetrahydro-1-methyl-5-[[2-(1-naphthyl)ethyl]amino]-2(1H)-quinolinone fumarate; 5-[[2-(4-chlorophenyl)ethyl]amino]-5,6,7,8-tetrahydro-1-(2-propenyl)-2(1H)-quinolinone hydrochloride; 5-[[2-(4-chlorophenyl)ethyl]amino]-5,6,7,8-tetrahydro-1-propyl-2(1H)-quinolinone fumarate; 5-[[2-(3,4-dichlorophenyl)ethyl]amino]-1-hexyl-5,6,7,8-tetrahydro-2(1H)-quinolinone fumarate; 5-[[2-(3,4-dichlorophenyl)ethyl]amino]-5,6,7,8-tetrahydro-1-(3-methyl-2-butenyl)-2(1H)-quinolinone maleate; 5,6,7,8-tetrahydro-1-methyl-5-[[2-(2-napthyl)ethyl]amino]-2(1H)-quinolinone and 5-[[2-(3,4-dichloro-phenyl)ethyl]amino]-5,6,7,8-tetrahydro-1-(2-[phenylethyl)-2(1H)-quinolinone. In addition, Bioorg. Med. Chem. Lett. 1999, 9, 2335-2338 (ibid) discloses 5-amino-, 5-n-butylamino- and 5-2-(phenyl)ethyl-5,6,7,8-tetrahydro-2(1H)-quinolinones which also fall within formula IV. However, certain compounds having a nucleus of general formula IV are novel. In another aspect, the present invention therefore provides a compound having a nucleus of the general formula 
which may be substituted or unsubstituted, or a salt thereof, in which Q, R1 and xe2x80x94Wxe2x80x94Xxe2x80x94 are as defined above; with the provisos that
(i) when Q represents one carbon atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 where R2 represents a hydrogen atom or a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94 where R3 represents a benzyl group and the nucleus of formula IV is substituted at the 5-position by a methyl or benzyl group, then R1 is not a hydrogen atom;
(ii) when Q represents one carbon atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 where R2 represents a hydrogen atom or a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94 where R3 represents a benzyl group and the nucleus of formula IV is substituted at the 5-position by a methyl group, then R1 is not a methyl group;
(iii) when Q represents one carbon atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 where R2 represents a methyl group and the nucleus of formula IV is substituted at the 5-position by a methyl group, then R1 is not a hydrogen atom;
(iv) when Q represents one carbon atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 where R2 represents a methyl group and the nucleus of formula IV is unsubstituted, then R1 is not a benzyl, 2-phenylethyl, 2-(4-trifluoromethylphenyl)-ethyl, 2-(4-nitrophenyl)ethyl, 2-(4-chlorophenyl)ethyl, 2-(4-methoxyphenyl)ethyl, 2-(4-methylphenyl)ethyl, 2-(2,4-dichlorophenyl)ethyl, 2-(3,4-dichlorophenyl)ethyl, 2-(2,2-diphenyl)ethyl, 2-(1-naphthyl)ethyl or 3-phenylpropyl group;
(v) when Q represents one carbon atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 where R2 represents a propyl or 2-propenyl group and the nucleus of formula IV is unsubstituted, then R1 is not a 2-phenylethyl, 2-(4-chlorophenyl)ethyl or 2-(3,4-dichlorophenyl)ethyl group;
(vi) when Q represents one carbon atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 where R2 represents a hydrogen atom and the nucleus of formula IV is unsubstituted, then R1 is not a hydrogen atom, n-butyl or 2-phenylethyl group;
(vii) when Q represents one carbon atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 where R2 represents a hexyl, 3-methyl-2-butenyl, benzyl or 2-phenylethyl group and the nucleus of formula IV is unsubstituted then R1 is not a 2-(3,4-dichlorophenyl)ethyl group; and
(viii) when Q represents one carbon atom, xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94N(R2)xe2x80x94C(O)xe2x80x94 where R2 represents a methyl group and the nucleus of formula IV is substituted at the 7-position by two methyl groups, then R2 is not a 2-(4-chlorophenyl)ethyl group.
Compounds in which R1 is a hydrogen atom are preferred and compounds in which a compound as defined above in which Q represents one carbon atom, R1 represents a hydrogen atom and xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94 where R3 represents a benzyl group are particularly preferred. Of these, (xc2x1)-2-benzyloxy-5,6,7,8-tetrahydro-5-quinolinamine and salts thereof are especially preferred.
It should also be appreciated that compounds having a nucleus of general formula IV contain chiral centres and are therefore capable of existing as different optical isomers. The present invention thus also includes both the individual isomers and mixtures of such isomers. Moreover, U.S. Pat. No. 5,110,815 makes no mention of the possibility of such isomers and Bioorg. Med. Chem. Lett., 1999, 9, 2335-2338 only discloses racemic mixtures of such compounds. Thus, the invention also provides an enantiomer of a compound having a nucleus of the general formula 
which may be substituted or unsubstituted, or a salt thereof, in which Q, R1 and xe2x80x94Wxe2x80x94Xxe2x80x94 are as first defined above without provisos. The invention also provides the (S)- and (R) enantiomers of such compounds. Enantiomers in which R1 is a hydrogen atom are preferred, particularly enantiomers in which Q represents one carbon atom, R1 represents a hydrogen atom and xe2x80x94Wxe2x80x94Xxe2x80x94 represents a group xe2x80x94Nxe2x95x90C(OR3)xe2x80x94, where R3 represents a benzyl group. Of these, (S)-2-benzyloxy-5,6,7,8-tetrahydro-5-methyl-5-quinolinamine; (R)-2-benzyloxy-5,6,7,8-tetrahydro-5-methyl-5-quinolin-amine; (S)-(+)-2-benzyloxy-5,6,7,8-tetrahydro-5-quinolinamine and (R)-(xe2x88x92)-benzyloxy-5,6,7,8-tetrahydro-5-quinolinamine and salts thereof are especially preferred.
The enantiomerically pure compounds having a nucleus of general formula IV can be prepared from the corresponding racemic mixtures using conventional resolution techniques. One such technique involves the reaction of the racemic mixture with a pure enantiomer of an optically active acid, such as mandelic acid, in a suitable solvent, for instance, an alcohol such as methanol or ethanol. The desired enantiomerically pure compound may then be recrystallised from the solution. Enantiomerically pure dimeric compounds of the invention may be prepared from the appropriate enantiomerically pure compounds having a nucleus of general formula IV by reaction with a suitable compound of formula V.
The invention also provides a pharmaceutical composition which comprises a carrier and, as active ingredient, a dimeric compound as defined above. A process for the preparation of a pharmaceutical composition is also provided which comprises bringing a dimeric compound as defined above into association with a carrier.
A pharmaceutically acceptable carrier may be any material with which the active ingredient is formulated to facilitate administration. A carrier may be a solid or a liquid, including a material which is normally gaseous but which has been compressed to form a liquid, and any of the carriers normally used in formulating pharmaceutical compositions may be used. Preferably, compositions according to the invention contain 0.5 to 95% by weight of active ingredient.
The dimeric compounds of the invention can be formulated as, for example, tablets, capsules, suppositories or solutions. These formulations can be produced by known methods using conventional solid carriers such as, for example, lactose, starch or talcum or liquid carriers such as, for example, water, fatty oils or liquid paraffins. Other carriers which may be used include materials derived from animal or vegetable proteins, such as the gelatins, dextrins and soy, wheat and psyllium seed proteins; gums such as acacia, guar, agar, and xanthan; polysaccharides; alginates; carboxymethylcelluloses; carrageenans; dextrans; pectins; synthetic polymers such as polyvinylpyrrolidone; polypeptide/protein or polysaccharide complexes such as gelatin-acacia complexes; sugars such as mannitol, dextrose, galactose and trehalose; cyclic sugars such as cyclodextrin; inorganic salts such as sodium phosphate, sodium chloride and aluminium silicates; and amino acids having from 2 to 12 carbon atoms such as a glycine, L-alanine, L-aspartic acid, L-glutamic acid, L-hydroxyproline, L-isoleucine, L-leucine and L-phenylalanine.
Auxiliary components such as tablet disintegrants, solubilisers, preservatives, antioxidants, surfactants, viscosity enhancers, colouring agents, flavouring agents, pH modifiers, sweeteners or taste-masking agents may also be incorporated into the composition. Suitable colouring agents include red, black and yellow iron oxides and FD and C dyes such as FD and C blue No. 2 and FD and C red No. 40 available from Ellis and Everard. Suitable flavouring agents include mint, raspberry, liquorice, orange, lemon, grapefruit, caramel, vanilla, cherry and grape flavours and combinations of these. Suitable pH modifiers include citric acid, tartaric acid, phosphoric acid, hydrochloric acid and maleic acid. Suitable sweeteners include aspartame, acesulfame K and thaumatin. Suitable taste-masking agents include sodium bicarbonate, ion-exchange resins, cyclodextrin inclusion compounds, adsorbates or microencapsulated actives.
The dimeric compounds and compositions of the invention are also useful as cholinesterase inhibitors and inhibit both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). However, they are more active against AChE than BChE. The invention therefore also provides a dimeric compound or a composition as defined above for use as a cholinesterase inhibitor or for use in the treatment of a condition which is ameliorated by cholinesterase inhibition. Such conditions include neurodegenerative diseases, especially Alzheimer""s Disease and myasthenia gravis. Indeed, the dimeric compounds and compositions of the invention are particularly useful for relieving the memory dysfunction associated with Alzheimer""s. Disease. A suitable dosage for the dimeric compounds and compositions of the invention in the treatment of, for example, Alzheimer""s Disease is from 0.02 to 0.20 mg, preferably 0.05 to 0.15 mg, once or twice daily, assuming that the patient has an average body weight of 50 kg.
Use of a dimeric compound or a composition as defined above for the manufacture of a medicament for use as a cholinesterase inhibitor or in the treatment of a condition which is ameliorated by cholinesterase inhibition is also provided. Similarly, a method for inhibiting cholinesterase activity in a mammal afflicted with a condition which is ameliorated by cholinesterase inhibition which comprises administering to the mammal in need thereof an amount of a compound as defined above or a composition as defined above effective to inhibit said activity is also provided.
The invention is further illustrated by the following examples. In these examples, 1H and 13C-NMR spectra were recorded on a BRUKER ARX-300 spectrometer (1H at 300.13 MHz, 13C at 75.48 MHz). All chemical shifts are expressed in ppm and the coupling constants in Hz. Melting points were determined with Electrothermal 9100 melting point apparatus and are uncorrected. Chemical ionization (CI) mass spectra were acquired using either ammonia or methane as the reagent gas. Elemental analyses were performed by Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences (Shanghai, P. R. C.). Optical rotation was measured with Perkin Elmer 241 Polarimeter. Analytical thin-layer chromatography (TLC) was performed with aluminum sheets coated with RDH silica gel 60 F254. Flash column chromatography was performed using Merck silica gel 60 (230-400 mesh). High-performance liquid chromatography (HPLC) was performed on Lichrosorb(copyright) RP Select B column (0.4xc3x9725 cm, 5 xcexcm), detection at 303 or 337 nm, gradient elution using solvent mixtures of A=H2O+0.1% CF3COOH, B=20% A+80% CH3CN operated at the program of A: B=100:0 at 0 minutes to 10:90 at 30 minutes, flow rate 1.0 m/min.
All moisture-sensitive reactions were conducted in oven dried (150xc2x0 C.) glassware under an atmosphere of dry nitrogen. Gastight syringes were dried in vacuo at room temperature before use in these reactions. Tetrahydrofuran was distilled from sodium-benzophenone ketyl immediately prior to use. All chemicals were commercial products and were used as received.